Its been a while since i contributed to the forum so i decided to do so today. After some experimentation, ive come to a conclusion on how efficient the stock IC and turbo are.

About two months ago i had my engine rebuilt and streetported by Kevin at RR. The engine came back spectacular, and the ports to me seemed to be exceptionally bigger (exhaust port). Well before my streetport, here was my car's boost levels at 100% throttle.

1st gear - 7psi
2nd gear - 10psi
3rd gear - 13psi
4th gear - 1bar
5th gear - never tested.

On my SAFC, the max airflow was 51.0%.

After breaking in my SP, i decided to take it for a test run. Once it hit 4k rpm, i felt a little pull, but then from 4k to 6k was just blowing air. 6k-8k was hard acceleration...this is at 100% throttle. HERE is where the problem comes up.

Last night i did a little experimentation on a semi highway. from a stop, i put it in 1st gear and did a 1-2 gear run and my A/F was 51.0%...same as before, which is weird since my ports are significantly bigger. Also it probably took me at least 6-7 seconds to get to 60mph. It wasnt that the car wasnt fast..its just that the car didnt pull till 6k and it studdered in 2nd gear.

The reason behind it is w/ my new streetport here are my normal boost levels in all gears.

1st- 15psi
2nd - 15psi
3rd - 15psi
4th - 15psi.

but, the 15psi spike is from 4k to 6k rpm, so i did a little further experiment. from a stop i gave it 70% throttle (per SAFC) and my max psi was only 12psi, but it took longer to get there since my throttle plates werent open all the way. the car pulled mad crazy from 5k up at 12psi (didnt spool 12 till 5k since i wasnt flooring it). A/F was at 52.0% at 70% throttle (SAFC told me this)

so my Theory is: On a streetported engine, if you make the ports too big, there are two problems. The stock turbo creates a restriction because of the impeller housing. The reason the car wasnt pulling at 15psi was because the turbo was out of efficiency rating, and the stock IC wasnt cooling the air enough. People, the stock turbo is a POS when it comes to boost above 13psi. I know i dont have the papers to back it up, but through simple experimentation, the car pulled harder at 12psi longer then 1 bar did. The reason the car pulled hard at 6krpm was that was when my big wastegate bled off the boost and was around 12-13psi (see a trend, lower boost = more power because of efficiency).

So my lesson is, On a turbo motor with full 3" intake/exhuast, a big streetport isnt capable of acheiving its maximum power potential without a bigger turbo for the naturally higher boost levels (T04 hybrid at least) and a FMIC that will be able to cool the temperatures of the compressed air more efficiently then the stock TMIC.

I dont have the $$ for a full T04 + ECU, so im investing in a stage 4 BNR supercars turbo after i talk to bryan about it. At least then 15psi will be efficient and net me hopefully ~330-350rwhp.

Thanks for listening and share comments if u need

Jeff

 

That sounds pretty much right to me. If you wanted to get a little more out of the stock turbo on the top end you could clip it a little bit. But I wouldn't be boosting that much with the stock turbo. I would think that with that much pressure the stock turbo wouldn't last very long. That's what almost twice stock boost. Just my opinion though. You may have significant data to prove that it works, and obviously you're having success with it right now. So good luck and save up some more dough so you can get a new turbo and really utilize the port job . Enjoy.

- Steiner

 

I actually think you have a bigger problem, I know of at least one person with a S5 extend port running a stock S4 turbo and IC, boosts to ~15psi and make some quite impressive power 180kw+ on an australian dyno.

It is however, NOT running a standard computer, possibly this is your problem?

 

i have no doubt that he could make that amount of power at all. Im sure though that a fully tuned standalone will help in that power output. How much would that be in standard hp?

from 6-8k rpm i definatly feel the power..probably 260rwhp, but im sure i'd be making more EFFICIENT power with a turbo/intercooler that 15psi is nothing out of the ordinary for

 

That's some very interesting data...
I dunno how reliable the readings off the S-AFC are though.


-Ted